$_POST is empty after form submit

Plz try and add names to the input types like

<input type="text" id="inputLastname" name="inputLastname" placeholder="Last name">

Now check the $_POST variable.

Your inputs don't have name attributes. Set those:

<input type="text" id="inputName" placeholder="First name" name="first_name" />
<input type="text" id="inputLastname" placeholder="Last name" name="last_name" >

Also, look at the way you detect a form submission:

if(isset($_POST['send']))

You check if the submit button is present in the post data. This is a bad idea because in the case of Internet Explorer, the submit button won't be present in the post data if the user presses the enter key to submit the form.

A better method is:

if($_SERVER['REQUEST_METHOD'] == 'POST')

Or

if(isset($_POST['first_name'], $_POST['last_name']))

More info - Why isset($_POST['submit']) is bad.